Rhizosphere microbiome-mediated modulation of nitrogen use efficiency in Oryza sativa L. under water-deficit stress: Mechanistic insights and agronomic implications
Abstract
Water-deficit (WD) stress is one of the most pervasive abiotic constraints limiting irrigated rice (Oryza sativa L.) productivity in the deltaic agroecosystems of peninsular India. The rhizosphere microbiome comprising diazotrophic bacteria, phosphate-solubilising bacteria (PSB) and plant growth-promoting rhizobacteria (PGPR) represents an underexploited biological resource for improving nitrogen use efficiency (NUE) under combined edaphic and hydric constraints. We conducted a two-factorial pot experiment (completely randomised design, (CRD)) at the Research Farm of the School of Agriculture, SR University, Warangal, Telangana, India (17.98058° N, 79.59429° E; altitude ≈ 260 m above mean sea level (AMSL)), during the 2024 kharif season (June–November 2024), comprising six microbial inoculation treatments (T0, uninoculated control; T1, Bradyrhizobium japonicum; T2, Azospirillum brasilense; T3, PSB consortium; T4, tripartite consortium; T5, tripartite consortium + 75 % recommended dose of nitrogen (N)) crossed with two soil-moisture regimes (100 % field capacity, well-watered (WW); 50 % field capacity, WD. Consortium inoculation (T5) preserved rhizosphere microbial diversity, sustained N-cycling enzyme activities and improved N assimilation enzyme activities and grain yield relative to the uninoculated control under WD stress, with the largest relative gains recorded for NUE and nitrate reductase activity. These agronomic improvements were accompanied by measurable increases in soil urease activity and microbial biomass N. Overall, the results indicate that rhizobacterial consortia can meaningfully buffer rice NUE and yield against water-deficit stress, offering a biologically grounded, field-testable strategy for reducing reliance on synthetic N fertiliser in drought-prone deltaic rice systems, pending confirmation under open-field conditions.